package com.lazy.lib.util;

/**
 * 从C代码移植过来的CRC16-CCITT算法
 * @author grind
 *
 */
public class CRC16_CCITT {

	private static char[] ccitt_table = {
	    0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7,
	    0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF,
	    0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6,
	    0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE,
	    0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485,
	    0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D,
	    0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4,
	    0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC,
	    0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823,
	    0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B,
	    0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12,
	    0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A,
	    0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41,
	    0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49,
	    0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70,
	    0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78,
	    0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F,
	    0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067,
	    0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E,
	    0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256,
	    0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D,
	    0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
	    0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C,
	    0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634,
	    0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB,
	    0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3,
	    0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A,
	    0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92,
	    0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9,
	    0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1,
	    0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8,
	    0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0
	};

	/**
	 * compute crc16 ccitt 校验值
	 * @param q
	 * @param index 偏移值,q的开始索引
	 * @param len 必须小于等于q.length - index
	 * @return
	 */
	public static int crc_ccitt(byte[] q, int index, int len)
	{
		short crc = (short)0xffff;
	
	    
	    for (int i = 0; i < len; i++) {
	        crc = (short) (ccitt_table[(crc >>> 8 ^ q[i+index]) & 0xff] ^ (crc << 8));
	    }

	    
	    return ((~crc)^0xffff) & 0xffff;
	
	}
	
	public static void main(String[] args) {

		byte[] test = { (byte) 'h', (byte) 'e', (byte) 'l', (byte) 'l', (byte)'o' };
		
		byte[] test2 = { 0x00, 0x00, 0x00, 0x1f, 0x00, 0x00, 0x00, 0x00,
				          0x10, 0x02, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00,
				          0x00, 0x01, 0x17, 0x75, (byte) 0x87, 0x6a, 0x43, 0x09,
				          0x35, 0x4d, 0x0d};
		byte[] test3 = {
				0x00, 0x00, 0x00, 0x48, 0x00, 0x00, 0x00, 0x00,
				0x10, 0x01, 0x00, 0x01, (byte) 0xae, 0x10, 0x01, 0x00,
				0x00, 0x01, 0x15, 0x15, 0x6d, (byte) 0xb0, 0x60, 0x32,
				(byte) 0x91, 0x10, (byte) 0xfa, 0x21, 0x50, 0x18, 0x4a, (byte) 0xd0,
				(byte) 0x88, (byte) 0x95, (byte) 0xb7, 0x7b, (byte) 0xe7, (byte) 0xbb, (byte) 0xd0, 0x30,
				0x1d, (byte) 0xa8, 0x43, (byte) 0xb0, (byte) 0xfd, (byte) 0x99, 0x49, (byte) 0xb6,
				0x68, (byte) 0xff, (byte) 0x99, 0x41, (byte) 0xf5, (byte) 0xda, (byte) 0xa4, 0x19,
				0x11, (byte) 0xac, 0x26, 0x7f, (byte) 0xd9, (byte) 0xb9, 0x79, 0x5c,
				0x0c, (byte) 0xf5, (byte) 0xf9, (byte) 0xf0
		};
		
		byte[] test4 = {
		        (byte)0x5b, 
		        (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x73, (byte)0x00, (byte)0x00, (byte)0x00, (byte)0x04, (byte)0x12, (byte)0x00, (byte)0x00, (byte)0x04, (byte)0xe2, (byte)0x4c, (byte)0x01,
		        (byte)0x00, (byte)0x00, (byte)0x01, (byte)0x15, (byte)0x15, (byte)0x6d, (byte)0xb0, (byte)0xab, (byte)0xe6, (byte)0x7e, (byte)0x58, (byte)0xf9, (byte)0x2a, (byte)0x56, (byte)0x1e, (byte)0x7f,
		        (byte)0xe6, (byte)0xbf, (byte)0xad, (byte)0x85, (byte)0x49, (byte)0xd6, (byte)0x95, (byte)0xe2, (byte)0x02, (byte)0x2b, (byte)0x86, (byte)0x7a, (byte)0x80, (byte)0xc1, (byte)0xaa, (byte)0x7b,
		        (byte)0x84, (byte)0x68, (byte)0xc2, (byte)0xaa, (byte)0x73, (byte)0xc5, (byte)0xea, (byte)0x93, (byte)0x2f, (byte)0x11, (byte)0xac, (byte)0x26, (byte)0x7f, (byte)0xd9, (byte)0x8e, (byte)0x49,
		        (byte)0x6d, (byte)0x3d, (byte)0xcd, (byte)0xda, (byte)0x7c, (byte)0xfd, (byte)0xf5, (byte)0x93, (byte)0xbb, (byte)0x09, (byte)0x12, (byte)0xfd, (byte)0xbb, (byte)0x3a, (byte)0x73, (byte)0x30,
		        (byte)0x85, (byte)0x38, (byte)0x32, (byte)0x64, (byte)0x9f, (byte)0x70, (byte)0xe8, (byte)0x79, (byte)0x04, (byte)0x03, (byte)0x8c, (byte)0x62, (byte)0xf5, (byte)0xc4, (byte)0x97, (byte)0xe8,
		        (byte)0xad, (byte)0x3b, (byte)0xa0, (byte)0x9b, (byte)0xa2, (byte)0x16, (byte)0x7c, (byte)0x22, (byte)0x46, (byte)0x01, (byte)0xf6, (byte)0x93, (byte)0xb4, (byte)0x52, (byte)0x16, (byte)0x22,
		        (byte)0x2f, (byte)0x08, (byte)0x5d
		};

		// int code = crc_ccitt(test2, 0, 23);
		//int code = crc_ccitt(test3, 0, 68);
		int code = crc_ccitt(test4, 1, test4.length-4);

		// 以下是为了测试方便进行的处理，因为char数据类型很多是不可显示的
		String str = Integer.toHexString(code);
		System.out.println("code:" + str);
	}

}
